Fiber optic modules interface optical fibers to electronic circuitry transducing communication by light or photons with communication by electrical signals. A fiber optic module may be a fiber optic receiver, transmitter or transceiver including both receive and transmit functions. The fiber optic receiver, transmitter and transceiver each have optical elements (OE) and electrical elements (EE). The fiber optic transmitter OE includes an emitter (such as a semiconductor LED or Laser) mounted in a package and an optical coupling element for coupling light or photons from the OE into the optical fiber. The type of semiconductor laser (light amplification by stimulated emission of radiation) may be a vertical cavity surface emitting laser (VCSEL). The fiber optic receiver OE includes a photodetector (such as a photodiode) mounted in a package and an optical coupling element for coupling light or photons from the optical fiber into the photodetector. The EE for each includes integrated circuits, other active elements and passive elements mounted on a substrate such as a printed circuit board (PCB) or ceramic. The OE and EE are connected electrically at the emitter and photodetector.
Because of the high modulation frequencies utilized in fiber optic communication, crosstalk between receive and transmit signals and electromagnetic interference (EMI) is of concern. In order to reduce EMI, shielding of the high frequency electrical components is required which is usually accomplished by attaching a metal shield to the substrate of the fiber optic module and connecting it to ground. Rapidly increasing internet traffic has created a demand for low cost fiber optic devices with bandwidth capabilities up to 40 Gigabytes per second (Gbps) for distances up to 300 meters without sacrificing the quality of the fiber optic link. In order to meet the bandwidth demands, it is desirable to provide parallel fiber optic data links with four, ten or twelve channel VCSEL arrays each operating at 1.25 gigabytes per second (Gbps), 2.5 Gbps or up to 10 Gbps. Each VCSEL in the VCSEL array is, spaced apart at 250 μm and coupled in parallel to a fiber optic ribbon cable. Such small spacing between each VCSEL in a VCSEL array allows for compact packaging of a VCSEL array which can be used in a multiple channel laser transmitter or transceiver. However, the tightly packed VCSELs in the VCSEL array having such small spacing there between introduces some challenges. One challenge which is difficult to overcome is separately monitoring the output power of each VCSEL in the VCSEL array when they are so tightly spaced and packaged together.
To maintain the quality of multiple channels providing multiple fiber optic data links, monitoring the output power of each individual VCSEL is important in order to assure signal quality. It is desirable to maintain a constant output power over temperature variations and time. To maintain a constant output power, each individual VCSELs operation needs to be separately monitored and optimized over time due to temperature variations, aging, and other effects. Additionally, the close spacing of the VCSELs in a VCSEL array aggravates the difficulty of placing EE components and interconnections on a printed circuit board. Additionally, the close spacing of VCSELs in the VCSEL array complicates any optical alignment needed between EE and OE components and the fiber optic cable. A VCSEL array necessitates five dimensional alignment between the EE and the OE in the X, Y, Z axes and along the axes of rotation and of tilt for each VCSEL in the VCSEL array. To provide five dimensional alignment, expensive packaging and packaging tools are required.
Another disadvantage to VCSEL arrays is that power output is highly localized due to the tightly spaced VCSELs in the VCSEL arrays. Combining the output power of all the VCSELs in the VCSEL array, the combined output power exceeds IEC Class-1 eye safety limit. This necessitates the special handling of the data link modules when powering the VCSEL array such as when plugging it into a printed circuit board. Otherwise, harm may result to a user's eyes if the user accidentally looks into the laser beams from the VCSEL array.
For commercial acceptance, fiber optic modules generally must comply with existing industry standards such as the Hot pluggable Gigabit Interface Converter (GBIC) de facto industry standard. The details of the GBIC standard are set forth in SFF Committee Proposed Specification for GBIC (Gigabit Interface Converter), Rev. 5.4, Aug. 16, 1999, the disclosure of which is incorporated herein by reference. Because of the relatively large size of GBICs, end users desire more compact, high throughput fiber optic transceivers. Particularly, end users desire a GBIC in a small form pluggable (SFP), LC package.
It is desirable to improve upon the prior art. There is a need to support high bandwidth links whose output power can be monitored and optimized over temperature variations and time, while overcoming EMI and eye safety concerns. There is a need to provide simplified alignment in a multichannel fiber optic module to reduce costs. Moreover, there is a need for fiber optic modules meeting these needs, yet still conforming to industry standards.